Engraved identification cards are known and can be engraved utilizing any one of a number of electronic engraving systems such as those disclosed in Noda, et al., U.S. Pat. No. 3,950,608 or Wada, et al., U.S. Pat. No. 4,052,739 or any other similar engraving system. Utilizing an electronic engraving system an image can be engraved in an identification card blank by making a multiplicity of scores through one opaque colored plastic layer of the card blank into a second, different colored opaque plastic layer of the card blank. By varying the depth of the engraved scorings, the width of the regions between the scores will be varied to generate light and dark regions which make up the desired image. A complete description of such identification cards and the method of making them is disclosed in Oka, et al., U.S. Pat. No. 3,897,964 and Oka, et al., U.S. Pat. No. 3,930,924, the disclosures of which are hereby incorporated by reference.
Heretofore, to provide a useful identification card, it was necessary to initially provide a card blank where an opaque base of one color was overlaid with an opaque layer of a contrasting color so that light impinging on the engraved surface of the card would be variably reflected back to the eye of the observer according to the location and amount of top layer removed to form an observable image.
The present invention comprises a novel identification card and method for making the same by disposing a dye precursor in the form of color-changeable solution (1) over the entire surface of a card blank prior to engraving, (2) in the engraved grooves of a pre-engraved card, or (3) on the non-engraved surface regions of a pre-engraved card to form a solid color-changeable layer, and thereafter applying radiant energy for a period of time to effect a change in the color of the color-changeable layer to provide a contrast between the color-changeable layer and the base layer. Initially, the color-changeable layer will preferably be the same color as the base layer. To assure such a color coordination, it is possible to pigment the base layer to match the color of the color-changeable layer.
Preferred pigmenting compounds which cause a color change upon exposure to ultraviolet light are the triphenylmethane type dyes which are formed by a free radical initiated oxidation reaction of a near colorless aromatic amine dye precursors such as diphenylamine. The coatings are applied to vinyl or polyester base card stock. The ultraviolet light sensitivity of these compounds and the resultant color changes are disclosed in Wainer, U.S. Pat. Nos. 3,042,515 and 3,042,516, Sprague, U.S. Pat. No. 3,046,209 and Fidelman, U.S. Pat. No. 3,114,635, the teachings of which are hereby incorporated by reference.
Further, the present invention comprises a multi-layered engraved identification card and a method for making the same wherein the multi-layered identification card includes a base layer of a first color and a color-changeable layer of a second color disposed on and bonded to selected regions of the base layer. Preferably, the color of the color-changeable layer is initially the same as the first color of the base. The color of the color-changeable layer is changeable to a third color which contrasts with the first color upon the exposure of the color-changeable layer to radiant energy for a specified period of time.
In one embodiment, the color-changeable layer is diffusion-bonded to the base layer. In another embodiment, the color-changeable layer is bonded to the base by a molecular cross-linking.
The color-changeable layer is initially applied as a solution which may be a dispersion of particulated solids to one surface of the base. The solution includes a resin, a plasticizer for modifying the base material to allow diffusion of the resin thereinto, a coloring agent for causing the second color to change to the third color upon being subjected to radiant energy and a free radical-forming initiator for the reaction. Finally, the solution includes a solvent in which both the base and the resin are soluble.
In a preferred embodiment of the invention, the coloring agent is diphenylamine, although other aryl amines, carbazoles and indoles which are sensitive to certain forms of radiation such as aryl amines having the general formula ##STR1## wherein R represents hydrogen, alkyl, aryl and aralkyl; R.sub.1 represents alpha-naphthyl and beta-naphthyl; and R.sub.2 represents an alkyl, aryl or arylalkyl group such as diphenylamine, N-methylaniline, N,N-dimethylaniline, N-ethylaniline, N,N-diethylaniline, phenyl-alphanaphthylamine, phenyl-beta-naphthylamine, triphenylamine, N-methyldiphenylamine, N-benzylaniline, N,N-dibenzylaniline, N-benzyldiphenylamine and N-beta-hydroxyethylaniline.
Additional color-changing agents include carbazoles having the formula ##STR2## wherein R.sub.3 represents hydrogen or an alkyl, aryl, aralkyl, alkoxy, halogen or dialkylamino group, the same or different, and R represents the components described with respect to formulate (1); such as carbazole, N-ethylcarbazole, N-methylcarbazole, N-phenylcarbazole and N-benzylcarbazole.
Additional color agents are indoles represented by the formula ##STR3## wherein R and R.sub.3 represent the components described with respect to formulae (1) and (2); such as indole, 2-methylindole, 1,2-dimethylindole, 1-phenylindole and 4-chloroindole. In addition, other compounds or materials which change color upon exposure to radiant energy and which are capable of binding to polymeric identification cards in the manner described, may be used without departing from the true spirit of the invention.
In this regard, the preferred embodiment describes the use of ultraviolet radiation having a wavelength of from about 3,500 to about 5,000 Angstroms to effect the color change, other forms of electromagnetic waves such as gamma rays, X-rays, visible light rays, infrared light or microwaves may be used.
In addition, the preferred free radical initiator is carbon tetrabromide, although other halogen-containing materials having the formula EQU R--CX.sub.3 ( 4)
wherein R represents hydrogen, a halogen or an alkyl, arylalkyl or aryl group which may be substituted or unsubstituted, and each X represents a halogen atom, namely, chlorine, bromine or iodine and may be the same or different from one another, as well as other free radical formers known in the art.
The solution may further comprise any additional pigmenting or dyeing agent for altering the color of the color-changeable pigment to a preselected different initial color as to match the color of the base.
It should be noted that the identification card of the present invention offers substantial advantages over cards produced by the multi-colored layering or pigmenting techniques heretofore known. Due to the nature of the liquid carrier provided for the irradiation-sensitive material, the color is attached to the base card by molecular bonding and thus provides a more durable engraved card. In addition, the color which results from the chemical change is irridescent and not obtainable or reproducable with pigments. Thus, the identification card is both attractive and forgery-proof.
The carrier solution may further comprise any additional pigmenting or dyeing agent for altering the color of the color-changeable pigment to be a preselected different initial color as to match the color of the base.
A method of making and an identification card having a base and a color-changeable layer includes initially providing a vinyl, polyvinyl chloride, polyester or Mylar.TM. plate or base having a first color. A solution is next prepared comprising a color-changing material as heretofore described, a free radical former, a binder for enabling diffusion bonding of the solution to the base, and a solvent in which both the resin and the base are soluble. The prepared solution is next applied as a layer to the base and the solvent allowed to evaporate causing a solid, color-changeable layer to be formed on and diffusion bonded to the base. The resultant blank card is then engraved through the color-changeable layer into the base after which the color-changeable layer is exposed to radiation to effect a change in color of the color-changeable layer. A contrast between the engraved and non-engraved portions of the engraved identification cards is thereby provided.
In accordance with another embodiment of the invention, the base is initially engraved with the solution being applied to the non-engraved surface regions. In this embodiment, the solution is provided with increased viscosity by the addition of suitable particulate fillers to prevent the solution from flowing into the engraved depressions. After the solvent is evaporated, the card is irradiated to cause a "developing" of the color-sensitive layer to effect the contrast desired between the color-changeable layer and the base.
In still a third embodiment of the invention, the base is initially engraved and the color-changeable solution thinned to have a sufficiently low viscosity to flow into and fill the engraved grooves but leave the non-engraved surface regions of the base exposed. Again, the solvent is allowed to evaporate thereby forming a hard color-changeable layer which changes color when irradiated.